In recent years, the combination of digital signal process (DSP), coherent detection, and spectral efficient high-level modulation format has been favored to increase network capacity. Recent developments in high speed electronic DSP technology have enabled compensation for fiber optic impairment electronically. The long-haul network has begun to utilize 100G coherent transmission systems, and metro network will follow the steps of long-haul network at a time delay of two to three years, as it did in the past decades. However, metro 100G coherent transmission network is much more sensitive to the footprint, power consumption and cost of the coherent transceiver modules. Silicon photonics technology is the key to tackle cost and footprint. With optical integration on silicon-on-insulator (SOI) platform, cost may be reduced by minimizing assembly touch points, mechanical adjustments, test apparatuses and the requirement of materials and separated devices.